REE Abundances Research Articles

A mineralogical-geochemical-petrological study of deformed carbonatites from Padu-Nongryngkoh Jaintia and East-Khasi Hills, Meghalaya, Northeastern India

The study presents the first mineral chemistry, geochemistry, and petrogenesis of the magnesio-carbonatite dykes from the recently identified Padu-Nongryngkoh region, Meghalaya (India). In the field, carbonatites occur as dykes emplaced in the intensly deformed and layered basement of gneissic rocks. Padu Carbonatites primarily consist of calcites and dolomites along with varied proportions of apatite, forsterite, phlogopite, spinel, pyrochlore, ilmenite, magnetite and zircon. Apatites of these carbonatites show magmatic characteristics with marked enrichment of chlorine and heavy rare earth elements. However, these carbonatites display lower REE concentrations compared to the average REE abundances of global carbonatites. These carbonatites are marked by extreme depletion of Ni, Ti, Rb, Nb, Ta, Zr and Hf. These carbonatites are associates with an episodic network of dykes and sills in the Padu-Nongryngkoh-Jarain area formed by the possible upwelling of the Kerguelen Plume. Low REEs in the Padu carbonatites may be due to either lack of REE replenishment in the magma source, or due to a differentiates alkaline hydrated melt as the source for these rocks.

Selective metasomatism of ultramafic cumulates within Archean supracrustal sequences

The Neoarchean Storø Supracrustal Belt in SW Greenland comprises a sequence of mature quartzite, metapelite, amphibolite, and ultramafic rocks that underwent amphibolite facies metamorphism during the amalgamation of the Mesoarchean Akia Terrane and the Eoarchean Færingehavn Terrane. In this belt, tourmaline is found in a transition zone between ultramafic and metapelitic rocks, but also occurs as orbicules within the ultramafic rocks. These tourmaline orbicules hosted by ultramafic rocks are reported for the first time in the North Atlantic craton, thus indicating a unique formation mechanism. We conducted a comprehensive examination of the petrology, whole-rock and mineral chemistry, and oxygen isotope compositions from borehole samples in the Storø Supracrustal Belt, to elucidate the metasomatic events associated with the formation of the orbicular tourmalines. The Storø ultramafic rocks have high MgO, Cr, and Ni contents, with low abundances of REE and HFSE, and preserve a typical cumulate texture. These features are similar to those of ultramafic cumulates found in other Archean supracrustal belts, suggesting a cumulate origin for the Storø ultramafic rocks. Furthermore, the morphology and composition of the tourmaline orbicules within these cumulates indicate that they originated from melts with high boron and high water concentrations that infiltrated the ultramafic rocks. The main factor influencing the morphology of the tourmaline orbicules is the silicification of the ultramafic rocks, driven by their lower chemical potential of SiO2 compared to the surrounding rocks. This silicification process, in combination with compositional variations of cumulates during fractional crystallization, has contributed to the geochemical diversity observed in Archean ultramafic rocks. Thus, it is crucial to understand the effects of such selective metasomatism on Archean ultramafic rocks, as this will facilitate the extraction of original information preserved in the early rock record.

Influence of Organic Matter Thermal Maturity on Rare Earth Element Distribution: A Study of Middle Devonian Black Shales from the Appalachian Basin, USA

This study focuses on understanding the association of rare earth elements (REE; lanthanides + yttrium + scandium) with organic matter from the Middle Devonian black shales of the Appalachian Basin. Developing a better understanding of the role of organic matter (OM) and thermal maturity in REE partitioning may help improve current geochemical models of REE enrichment in a wide range of black shales. We studied relationships between whole rock REE content and total organic carbon (TOC) and compared the correlations with a suite of global oil shales that contain TOC as high as 60 wt.%. The sequential leaching of the Appalachian shale samples was conducted to evaluate the REE content associated with carbonates, Fe–Mn oxyhydroxides, sulfides, and organics. Finally, the residue from the leaching experiment was analyzed to assess the mineralogical changes and REE extraction efficiency. Our results show that heavier REE (HREE) have a positive correlation with TOC in our Appalachian core samples. However, data from the global oil shales display an opposite trend. We propose that although TOC controls REE enrichment, thermal maturation likely plays a critical role in HREE partitioning into refractory organic phases, such as pyrobitumen. The REE inventory from a core in the Appalachian Basin shows that (1) the total REE ranges between 180 and 270 ppm and the OM-rich samples tend to contain more REE than the calcareous shales; (2) there is a relatively higher abundance of middle REE (MREE) to HREE than lighter REE (LREE); (3) there is a disproportionate increase in Y and Tb with TOC likely due to the rocks being over-mature; and (4) the REE extraction demonstrates that although the OM has higher HREE concentration, the organic leachates contain more LREE, suggesting it is more challenging to extract HREE from OM than using traditional leaching techniques.

Silicate melt immiscibility as the cause of large-scale rare-metal mineralization in a peralkaline granite system: The case of the Baerzhe deposit in NE China

The Early Cretaceous peralkaline Baerzhe pluton hosts a potentially large REE-Nb-Zr-Be deposit in inner Mongolia, northeastern China. The mechanism responsible for the extreme enrichment of rare metals and rare earth elements in the pluton is still ambiguous. This study presents new evidence for silicate melt immiscibility as the key mechanism at Baerzhe using amphibole-group minerals from spherulite granite, which contains spherulites with abundant REE- and HFSE-bearing minerals. The spherulite from the transsolvus granite is composed of two distinct zones, i.e., a dark-colored core consisting of arfvedsonite aggregates and a light-colored rim consisting mostly of quartz and feldspar, rare amphibole, and abundant HFSE- and REE-bearing minerals. Four types of amphibole (AmpI, Amp-IIa, Amp-IIb and Amp-III) from the transsolvus granite and one type (Amp-IV) from the subsolvus granite are recognized, and all of them are magmatic fluoro-arfvedsonite. The earliest phase consists of euhedral inclusions of Amp-I within quartz or feldspar. They show an enrichment in HREEs relative to LREEs and a depletion in medium REEs, consistent with the REE pattern controlled by the mineral lattice. This implies that Amp-I likely formed in an initial homogeneous mel relatively depleted in REEs; thus, the mineral structure played a dominant role in REE partitioning. Compared with other types of amphiboles, Amp-IIa and Amp-IIb from the spherulite phase display the highest REE contents, with flat LREEs and MREEs and a slight upward HREE pattern. Combined with the significant accumulation of REE- and HFSE-bearing minerals in the rim zone, differences in REE patterns among different amphibole types imply that the spherulite crystallized in a volatile-rich silicate melt and was probably the product of silicate melt immiscibility. Interstitial Amp-III with lower REE contents from the matrix phase crystallized in the separate volatile-poor silicate melt. The Amp-IV from the subsolvus granite has the lowest CaO content, with strong depletion in LREEs relative to HREEs, suggesting a more evolved melt composition. It is concluded that silicate melt immiscibility may serve as an important key mechanism that occurred in the early stage of magmatic evolution, resulting in the enrichment of REEs and HFSEs, which played a critical role in the formation of large to giant ore deposits such as the Baerzhe deposit.

Oligocene–Miocene arc magmatic activities associated with the giant Reko Diq porphyry Cu–Au deposit, western Chagai arc, Balochistan, Pakistan

The Chagai belt to the north of the Afghan block and the east of the Iranian block in the western part of Pakistan is known for occurrence of Oligocene to Miocene calc‐alkaline magmatic belt. The present study discusses the characteristics of episodic magmatic activities that contributed to mineralization for the Reko Diq porphyry complex in the western part of the Chagai belt. U–Pb dating of zircons from volcanic rocks of the Reko Diq porphyry complex yielded ages of 25.8 ± 1.8 and 12.29 ± 0.44 Ma for two phases of magmatic crystallization. Geochemical analyses of whole‐rock rhyolite and dacite indicate that the rock units are peraluminous calc‐alkaline, derived from Andean‐type subduction. The magma was formed due to partial melting of the thickened mafic lower crust in a continental arc setting in relation to the subduction of the Neotethys along the Makran subduction zone. The abundance of zircons, Hf, REE, U/Pb and Th indicates high degrees of magmatic evolution. Moreover, the Sr and Nd isotopic data indicate the fractional contribution of depleted N‐MORB mantle to the Reko Diq magmas through bulk mixing with magmas derived from the lower continental crust. Short‐lived magmatic systems repeated magma injection, and various episodes of hydrothermal fluid flow have led to the formation of porphyry mineralization. Emplacement of the Reko Diq porphyry complex and related Cu–Au mineralization is associated with a series of tectonic–magmatic events at different episodes of the Oligocene–Miocene times.

Geochemistry of the North Gondwana Paleozoic Araba and Naqus formation siliciclastics, Sinai: implications for provenance, paleoweathering, and tectonic setting

ABSTRACT The Araba and Naqus formations in Ras Milan, Sinai, constitute part of the major continuous Paleozoic clastic belt stretching across northern Gondwana. They are sandstone-dominated successions, resting on Precambrian granitic basement, with lowermost thin basal polymictic conglomerate deposits (1–2 m), marking the unconformity. The Araba Formation section is composed mainly of varicoloured violet to reddish brown, fine to coarse-grained laminated and planner and overturned cross-bedded sandstones, while the overlying Naqus Formation is characterized by chaotically distributed poorly sorted quartz pebbles to cobbles within a moderately-sorted coarse- to medium-grained quartz arenite and by abundance and variety of large-scale tabular and trough cross bedding. Modal QFL classification of Araba and Naqus formation sandstones revealed that they are merely quartzose sandstones (quartz arenites). Geochemistry of the succession shows extremely wide compositional ranges for almost all major elements, but the Araba Formation is relatively enriched in SiO2, TiO2, Fe2O3*, Na2O, P2O5, and depleted in Al2O3, MgO, CaO and K2O relative to Naqus Formation. Only the Araba Formation samples are depleted in the transition elements Ni, Cr and Co and oppositely possess extreme enrichment in the HFSEs (i.e. Zr, Hf, Y, Nb, Ta, Th, U), whereas both formations show variable depletion in the LILE Rb, K and Ba, and excessive REE abundances relative to the PAAS and UCC, and LREE-enriched patterns with marked negative Eu anomalies. The provenance of the Naqus and Araba formations could be an earlier felsic magmatic source, which has undergone extensive sedimentary recycling. They possess high compositional maturity and were subjected to intensive to moderate weathering during humid climatic conditions. Passive margin tectonic setting is implied which denotes the derivation of Araba and Naqus formation siliciclastics from stable continental regions or plate interiors and deposition in intracratonic basins.

Gemological and Chemical Characterization of Gem-Quality Titanite from Morocco

Titanite is a widespread accessory mineral in igneous, metamorphic, and hydrothermal rocks, but few comply with gem-grade requirements. Previous studies on Moroccan titanite focused on elementary composition and U-Pb dating. In this study, two gem-grade titanites (MA-1 and MA-2) from the Moroccan Central High Atlas were investigated through gemological and chemical studies, including infrared spectrum, Raman spectrum, SEM-EDS, and LA-ICP-MS. Two titanite samples are yellow, transparent–translucent with a greasy luster, 3.5 and 2.5 mm long. MA-1 and MA-2 have similar gemological properties, the refractive index (RI) is beyond the range of the refractometer (>1.78), the specific gravity (SG) values fall in the range of 3.52~3.54 and both are inert to short-wave and long-wave UV radiation. The spectral characteristics have high consistency with the RRUFF database. The major elements’ composition shows a negative correlation between Al, Fe, V, and Ti, suggesting the titanites underwent substitutions such as (Al, Fe3+) + (F, OH) ↔ Ti + O. The titanite samples, characterized by a low abundance of REE (802~4088 ppm) and enriched in LREE, exhibit positive Eu (δEu: 1.53~7.79) and Ce (δCe: 1.08~1.33) anomalies, indicating their formation in a hydrothermal environment with low oxygen fugacity. The 238U/206Pb and 207Pb/206Pb ratios of the titanites yield lower intercept ages of 152.6 ± 2.2 and 151.4 ± 5.3 Ma (1s), consistent with their weighted average 206Pb/238U ages of 152.3 ± 2.0 and 150.7 ± 3.2 Ma (1s) respectively. The results of U-Pb dating are matched with the second main magmatic activities in the High Atlas intracontinental belt of Morocco during the Mesozoic to Cenozoic period. Moreover, the two titanite samples have almost no radiational damage. All the results show that the titanite from High Atlas, Morocco, has the potential to be a reference material for LA-ICP-MS U–Pb dating, but further experiments are needed to be sure.

Geochemistry of lanthanides in thermal waters of Issyk-Kul Lake Basin

The distribution and abundance of lanthanides in thermal waters of the northern Tien Shan (Issyk-Kul lake basin) were studied. Waters are represented by three types: Na-Cl-SO4-HCO3, Na-Ca-Cl-SO4 and Na-Ca-Cl, demonstrates alkaline pH (7.3–9.7) and Eh from -260 to +98 mV. Discharge temperature varies from 15 to 50oC, and total dissolved solids from 0.2 to 13.0 g/l. It is established that lanthanides (or rare earth elements, REE) concentrations vary from 0.07 to 0.81 ppb, the maximal concentrations relate to a Na-Ca-Cl water type, which demonstrates the influence of reverse ion exchange. The total concentration of rare earth elements roughly increases as pH decreases, implying that the absolute abundance of REE is totally controlled by pH conditions. The ΣREE concentrations in groundwater exhibit a high positive correlation (R=0.8) with the total dissolved solids contents indicating that ΣREE are well related to the salinity of the thermal water samples. The major ions HCO3, SO4, Ca, K, and Mg have minor associations with REE. The geochemical and geological data suggest that the principal REE source of the thermal waters is bedrock mineralogy and lithology. The distribution and abundance of REE in thermal waters of Issyk-Kul basin were studied for the first time.

The Raman spectrum of florencite‐(REE) [REEAl3(PO4)2(OH)6]: An integrated experimental and computational approach

AbstractFlorencite is a hydrous light rare‐earth elements (LREE) aluminium phosphate [REEAl3(PO4)2(OH)6], that amongst the REE‐rich minerals is quite common. The main end‐members are Ce‐, La‐ and Nd‐rich terms that were found in several genetic environments. Despite the large occurrence worldwide, to the authors' knowledge, florencite has attracted very few studies, particularly concerning the characterization of its Raman spectrum. We present a detailed study of the Raman spectrum of florencite, combining experimental measurements and theoretical calculations. Experimental Raman spectra (in the 100–1300 cm−1 spectral range) are measured on four florencite samples characterized by different chemical composition, that is, different REE abundance. The results highlight a remarkable coincidence between different Raman spectra measured on each sample, despite the significantly different chemical compositions in terms of their REE content. The same similarities were also observed in the computed spectra at the ab initio level; moreover, the calculations allowed the attributions of the different Raman signals to specific vibrational modes.

Biosorption of rare earth elements from luminophores by G. sulphuraria (Cyanidiophytina, Rhodophyta)

Lanthanides are indispensable constituents of modern technologies and are often challenging to acquire from natural resources. The demand for REEs is so high that there is a clear need to develop efficient and eco-friendly recycling methods. In the present study, freeze-dried biomass of the polyextremophile Galdieria sulphuraria was employed to recover REEs from spent fluorescent lamps (FL) luminophores by pretreating the freeze-dried biomass with an acid solution to favour ion exchange and enhance the binding sites on the cell surface available for the metal ions. Lanthanides were extracted from the luminophores using sulfuric acid solutions according to standardised procedures, and the effect of biosorbent dosage (0.5–5 mg/ml) and biosorption time (5–60 min) were evaluated. The content of individual REEs in the luminophores and the resulting algal biomass were determined using inductively coupled plasma mass spectrometry (ICP-MS). The most abundant REE in the luminophores was yttrium (287.42 mg/g dm, 91.60% of all REEs), followed by europium (20.98 mg/g, 6.69%); cerium, gadolinium, terbium and lanthanum was in trace. The best biosorption performances were achieved after 5 min and at the lowest biosorbent dosage (0.5 mg/mL). The highest total metal amount corresponded to 41.61 mg/g dried mass, and yttrium was the most adsorbed metal (34.59 mg/g dm, 82.88%), followed by cerium (4.01 mg/g); all other metals were less than 2 mg/g. The rapidity of the biosorption process and the low biosorbent dosage required confirmed this microalga as a promising material for creating an eco-sustainable protocol for recycling REEs.

Unlocking Dysprosium Constraints for China's 1.5 °C Climate Target.

Some key low-carbon technologies, ranging from wind turbines to electric vehicles, are underpinned by the strong rare-earth-based permanent magnets of the Nd, Pr (Dy)-Fe-Nb type (NdFeB). These NdFeB magnets, which are sensitive to demagnetization with temperature elevation (the Curie point), require the addition of variable amounts of dysprosium (Dy), where an elevation of the Curie point is needed to meet operational conditions. Given that China is the world's largest REE supplier with abundant REE reserves, the impact of an ambitious 1.5 °C climate target on China's Dy supply chain has sparked widespread concern. Here, we explore future trends and innovation strategies associated with the linkage between Dy and NdFeBs under various climate scenarios in China. We find China alone is expected to exhaust the global present Dy reserve within the next 2-3 decades to facilitate the 1.5 °C climate target. By implementing global available innovation strategies, such as material substitution, reduction, and recycling, it is possible to avoid 48%-68% of China's cumulative demand for Dy. Nevertheless, ongoing efforts in REE exploration and production are still required to meet China's growing Dy demand, which will face competition from the United States, European Union, and other countries with ambitious climate targets. Thus, our analysis urges China and those nations to form wider cooperation in REE supply chains as well as in NdFeB innovation for the realization of a global climate-safe future.

A systematic evaluation of titanite reference materials for optimizing trace element and U[sbnd]Pb analysis by LA-ICP-MS

Titanite (CaTiSiO5) is a commonly occurring and versatile accessory mineral with broad applications in petrochronology. In situ U-Pb and trace element analyses via SIMS and LA-ICPMS are routinely performed using a matrix-matched reference material for U-Pb and standard glasses (non-matrix matched reference material) for elemental abundance determination. We report U-Pb isotopic ratios and major and trace element concentrations for three titanite samples (Ecstall, McClure and FCT) which are commonly used as reference materials in petrochronology studies. In addition, we characterize two new samples which can potentially serve as matrix-matched reference materials for titanite trace element geochemistry (BLR-2 and BRA-1). Based on electron microprobe analysis, samples BLR-1 and BLR-2 are homogeneous and suitable for use as a primary reference material for trace element concentrations. Whereas Ecstall, McClure, and FCT titanite reference materials show high intra-grain heterogeneity, yielding relative standard deviations for most trace elements between 5% and 40%, with higher standard deviations for U of 70% for Ecstall (n = 26), 265% for McClure (n = 22), and 202% for FCT (n = 26). Therefore, we suggest that these grains are unsuited to serve as reference materials for trace element quantification. The BRA-1 titanite has low trace element concentrations and is chemically heterogeneous (total REE abundances of 40 ppm for the rim and 95 ppm for the core of the grain), thus is not suitable for standardization of chemical composition using LA-ICPMS. It is commonly asserted that a matrix-matched standardization provides a more robust downhole fractionation correction compared to a non-matrix matched standardization. However, it remains unclear which standardization approach (matrix-matched vs non-matrix matched/glass) is more accurate for titanite trace element quantification. To resolve this, we tested several standardization approaches for trace element quantification, comparing matrix-matched (BLR-1) and non-matrix-matched (NIST612) standardizations with different internal elemental standards (IES; Ca, Si and Ti) and without internal standardization (semi-quantitative). To provide an independent constraint on the accuracy of the various trace element standardization techniques we compared results to trace element concentrations obtained via solution Q-ICPMS on crushed BLR-2 and BRA-1 aliquots. The matrix-matched standardization using Si as the IES yields the best reproducibility of trace element concentrations followed by the matrix-matched reduction using Ti as the IES. Moreover, the matrix-matched semi-quantitative correction yielded the lowest weighted percentage of difference compared to reference trace composition quantified by solution ICPMS. Finally, in this contribution we also benchmark sampling-size for precise U-Pb dating of common-Pb rich phases like titanite.

Geochemical constraints on the provenance and tectonic setting of metasedimentary rocks from the South Delhi Supergroup, NW India: implications for tectonic evolution of western margin of the Aravalli orogen

ABSTRACT The provenance and tectonic setting of the Stenian (<1200 to 1015 Ma) metasedimentary sequences of the South Delhi Supergroup, NW India, are least understood and thus debatable. The results of this study show that the protoliths of the metasedimentary rocks received detritus dominantly from felsic sources, particularly from Mesoproterozoic granitoids exposed in northern and eastern India. The weathering indices suggest low to moderate weathering in the source areas and that the sediment compositions reflect mixing of provenance components having different compositions. Overall, the REE patterns of the South Delhi rocks are similar with variable negative Eu anomalies and absolute ∑REE contents. The low REE abundances in the quartzites are the consequence of quartz dilution during hydraulic sorting. The tectonic multidimensional discrimination diagrams suggest a passive margin setting for the South Delhi metasedimentary rocks, which is in consonance with the detrital zircon age spectra and regional geology of the western margin of Aravalli orogen, NW India.

Complexity and ambiguity in the relationships between major lunar crustal lithologies and meteoritic clasts inferred from major and trace element modeling

Clasts of feldspathic lithologies such as magnesian anorthosites, anorthositic troctolites, and granulites in lunar meteorites have greatly expanded knowledge of the lithologic diversity of the lunar crust. However, their origins and relationships to other major crustal lithologies such as the ferroan anorthosites, magnesian-suite, and alkali-suite are not fully understood. Here we present the results of phase equilibrium modeling using the MELTS and MAGFOX programs designed to investigate the origins of lunar crustal lithologies and petrologic connections between them. We show that the major and trace element compositions of the Mg- and alkali-suites are consistent with partial melting of hybridized sources and are inconsistent with decompression melting + assimilation models. Our results also show that the vertical trend in Mg# in mafic silicates vs. An# in plagioclase characteristic of feldspathic meteoritic lithologies and ferroan anorthosites can be produced by fractional crystallization of KREEP-free Mg-suite melts, but that these melts are not likely to contribute significantly to the composition of the global crust. Furthermore, we calculated potential parental melt compositions for these crustal lithologies using the abundances of REEs in plagioclase in FANs, the Mg- and alkali-suites, and clasts in feldspathic meteorites. Our results show that despite low bulk rock abundances of incompatible trace elements in many feldspathic lunar meteorites, parental melts with overall REE abundances similar to or in excess of KREEP are needed to reproduce the REE abundances in plagioclase in clasts from feldspathic lunar meteorites. However, the lack of a Na enrichment trend in their plagioclase compositions with decreasing Mg# requires very Na-depleted melts without a KREEP component. The available data regarding magnesian anorthosites, anorthositic troctolites, and granulites in lunar meteorites, and inferences made here regarding their parental melt compositions, lead to contradictory and ambiguous conclusions regarding their origins.

The ~1.1 Ga St. Ignace Island complex, Northern Ontario, Canada: Evidence for magma mixing and crustal melting in the generation of Midcontinent Rift-related bimodal magmas and implications for regional metallogeny

Abstract The St. Ignace Island complex in Northern Ontario is a package of dominantly felsic rocks emplaced within the upper portions of the Osler Volcanic rocks of the ~1.1 Ga Midcontinent Rift System. The Osler volcanic rocks are predominantly tholeiitic basalts intercalated with rare interflow sediments and rhyolites. The St. Ignace Island complex is a ~26 km2 stock with a felsic core of quartz-feldspar-phyric rhyolites and dacites and an outer ring of anorthosite and gabbro. Textures at a variety of scales within the rocks of the complex show clear evidence of the mingling and mixing of partially crystallized mafic and felsic liquids. Two multigrain (zircon/baddeleyite) fractions from a sample of the gabbro define a Discordia line with an upper intercept date of 1107±8.9 Ma. The core of the complex consists of dacites and rhyolites with similar REE abundances with negative Nb anomalies whereas the surrounding mafic rocks are gabbros to monzogabbros that are less LREE-enriched than the felsic rocks but with similar HREE. Felsic units have a narrow range of 87Sr/86Sri (0.7032-0.7045) and 143Nd/144Ndi (0.51051-0.51057) whereas the mafic end members have similar 87Sr/86Sri (0.7040-0.7061) but more radiogenic 143Nd/144Ndi (0.51067-0.51085). Very well-preserved silicate melt inclusions (MI), many completely glassy, were observed in quartz, clinopyroxene and some plagioclase phenocrysts from the complex. These represent some of the oldest unrecrystallized silicate melt inclusions described to date. Melt inclusions within quartz from the felsic volcanics are broadly rhyolitic in composition whereas MI from plagioclase in the mafic volcanics range from basalt to basaltic andesite; these felsic and mafic melt compositions are interpreted to represent the end-member liquids in the system and bulk rock analyses affirm mixtures of the two. Concentrations of Cu and Ag (in both mafic and felsic MI), and Mo (in felsic MI), are up to an order of magnitude higher in the mafic and felsic MI than in continental crust. Bulk rock metal concentrations are also significantly lower than in the MI, suggesting that the melt inclusions may preserve pre-eruptive metal tenors that were subsequently modified by sulfide saturation, degassing, or post-solidus hydrothermal alteration. The whole rock and MI geochemistry of the St. Ignace complex are broadly similar to the Central Osler Group and, given the broad similar ages, suggests they may have been derived from a similar mantle source, but distinct from the source of rhyolites in the Black Bay Peninsula. The negative Nb anomalies and negative εNd values for the St. Ignace complex are consistent with mixing with older continental crust during ascent and emplacement. The rocks of the St. Ignace Island complex likely formed as the result of emplacement of a large mafic magma chamber at the base of the Osler volcanic pile that triggered partial melting to generate the rhyolite end members. The felsic melts ascended to shallower levels in the crust where they mixed with mafic magmas derived directly from the deeper chamber. Generally, melt inclusions in the complex have very high Cu and Ag contents, similar to those observed in arc-related and extremely oxidized early rift-related rocks and may account for the world-class volcano-sediment-hosted Cu-(Ag) deposits within the rift and the presence of small porphyry-style deposits.

REE abundance, fractionation, and anomalies in sediments of the Cananéia-Iguape Estuarine-Lagoon Complex (CIELC), Brazil

REE abundance, fractionation, and anomalies in sediments of the Cananéia-Iguape Estuarine-Lagoon Complex (CIELC), Brazil

REE abundance, fractionation, and anomalies in sediments of the Cananéia-Iguape Estuarine-Lagoon Complex (CIELC), Brazil

REE abundance, fractionation, and anomalies in sediments of the Cananéia-Iguape Estuarine-Lagoon Complex (CIELC), Brazil

REE abundance, fractionation, and anomalies in sediments of the Cananéia-Iguape Estuarine-Lagoon Complex (CIELC), Brazil

REE abundance, fractionation, and anomalies in sediments of the Cananéia-Iguape Estuarine-Lagoon Complex (CIELC), Brazil

REE abundance, fractionation, and anomalies in sediments of the Cananéia-Iguape Estuarine-Lagoon Complex (CIELC), Brazil

REE abundance, fractionation, and anomalies in sediments of the Cananéia-Iguape Estuarine-Lagoon Complex (CIELC), Brazil

Hydrothermal alteration and the remobilization of rare earth elements during reprecipitation of nano-scale apatite in phosphorites

Sedimentary phosphorites enriched in rare earth elements (i.e., REE) are an important reservoir of these critical metals and may have the potential to resolve the global REE supply risk in the future, which is widely distributed around world. However, the occurrence and utilizability of REE in phosphorites remain contentious. In this study, multiple-scale analysis techniques were used to investigate the mineralogical and geochemical characteristics of typical REE-enriched phosphorites from Zhijin, SW China. The mineralization was divided into two stages: early fluorapatite (Fap1) that formed during the sedimentary–diagenetic stage, and late fluorapatite (Fap2) that formed during the hydrothermal alteration stage. The in situ REE geochemical data (i.e., quantitative data and mapping analysis) and scanning electron microscopy images show that Fap1 is the main REE host phase, because it is abundant and high REE concentration. Data obtained by both laser-ablation–inductively coupled plasma–mass spectrometry and high-resolution transmission electron microscopy reveal that most REE are resident in the lattice of nano-scale fluorapatite, which could be remobilized by hydrothermal fluids during the process of dissolution of nano-scale Fap1 and reprecipitation of micro-scale Fap2. In addition, the formation of synchysite-(Y) in the altered phosphorites involved reprecipitation of the mobilized REE. We suggest that F− and SO42− in fluids play a major role in the mobilization of REE in fluorapatite and that CO32− sourced from dolomite alteration contributes to the precipitation of REE. Our results indicate that REE in fluorapatite can be remobilized and further enriched by hydrothermal alteration to REE fluorocarbonates (the current predominant economic source of REE minerals). Overall, our results reveal that REE occur mainly in the lattices of fluorapatite and synchysite-(Y) in phosphorites, and provide new insights into the mineralization mechanism and industrial availability of REE-enriched phosphorites.